CHARACTERIZATION OF 3 TYPES OF HUMAN ALPHA(S1)-CASEIN MESSENGER-RNA TRANSCRIPTS

Here we report the molecular cloning and sequencing of three types of human alpha(s1)-casein transcripts and present evidence indicating that exon skipping is responsible for deleted mRNA transcripts. The largest transcript comprised 981 bp encoding a signal peptide of 15 amino acids followed by the mature alpha(s1)-casein sequence of 170 amino acids. Human alpha(s1)-casein has been reported to exist naturally as a multimer in complex with kappa-casein in mature human milk, thereby being unique among alpha(s1)-caseins [Rasmussen, Due and Petersen (1995) Comp. Biochem. Physiol., in the press]. The present demonstration of three cysteines in the mature protein provides a molecular explanation of the interactions in this complex. Tissue-specific expression of human alpha(s1)-casein was indicated by Northern-blot analysis. In addition, two cryptic exons were localized in the bovine alpha(s1)-casein gene.